Microcapsule and process for their production

Abstract

By using, in production of microcapsules, a partially esterified product of a styrene-maleic anhydride copolymer as an emulsifier, advantages are obtained that coloring of emulsion can be reduced/prevented at the time of emulsification and, when the microcapsules produced are used in a carbonless copying paper, a desensitizer component is not transferred to a lower paper and accordingly color development is not hindered.

What is claimed is: 
     
       1. A process for producing microcapsules containing a hydrophobic material as a core material, the process comprising the steps of dispersing or emulsifying a hydrophobic material in the form of discontinuous microparticles in an acidic aqueous solution containing a partially esterified product of a styrene-maleic anhydride copolymer, the partially esterified product of a styrene-maleic anhydride copolymer being used in a quantity of 2 to 20 parts by weight relative to 100 parts by weight of the hydrophobic material, adding a melamine-formaledhyde precondensate to the dispersion or emulsion obtained, and subjecting the resuting mixture to reaction in an acidic phase with heating to form a shell film on each microparticle. 
     
     
       2. A process for producing microcapsules according to claim 1, wherein the ester group of the partially esterified product of a styrene-maleic anhydride copolymer is selected from those having an alkyl group of 1 to 10 carbon atoms or an aralkyl group. 
     
     
       3. A process for producing microcapsules according to claim 1, wherein the esterification degree of the partially esterified product of a styrene-maleic anhydride copolymer is 50% or lower relative to total carbonyl group number. 
     
     
       4. A process for producing microcapsules according to claim 3, wherein the esterification degree is 5 to 50%. 
     
     
       5. A process for producing microcapsules according to claim 1, wherein the partially esterified product of a styrene-maleic anhydride copolymer is obtained by copolymerizing styrene monomer, maleic anhydride and a required quantity of a mono- or di-ester of maleic acid or by partially esterifying a styrene-maleic anhydride copolymer. 
     
     
       6. A process for producing microcapsules according to claim 1, wherein the melamine-formaldehyde precondensate is obtained by reacting melamine with formaldehyde in a molar ratio of 1 (the former)/1.5 (the latter) or in a lower molar ratio. 
     
     
       7. A process for producing microcapsules according to claim 6, wherein the molar ratio is 1/2 to 1/3. 
     
     
       8. Microcapsules produced by the process defined in claim 1.